linux-kernel - Re: [PATCH v10 1/3] cpufreq: Add mechanism for registering utilization update callbacks

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Message-ID: <1455900129.7375.231.camel@linux.intel.com>
Date:	Fri, 19 Feb 2016 08:42:09 -0800
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Juri Lelli <juri.lelli@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v10 1/3] cpufreq: Add mechanism for registering
 utilization update callbacks

On Fri, 2016-02-19 at 08:09 +0000, Juri Lelli wrote:
Hi Juri,
> > 
> Hi Rafael,
> 
> On 18/02/16 21:22, Rafael J. Wysocki wrote:
> > On Mon, Feb 15, 2016 at 10:47 PM, Rafael J. Wysocki <rjw@...ysocki.
> > net> wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> 
[...]

> However, I still don't quite get why we want to introduce an
> interface
> for explicit passing of util and max if we are not using such
> parameters
> yet. Also, I couldn't find any indication of how such parameters will
> be
> used in the future. If what we need today is a periodic kick for
> cpufreq
> governors that need it, we should simply do how we already do for RT
> and
> DL, IMHO. Also because the places where the current hooks reside
> might
> not be the correct and useful one once we'll start using the
> utilization
> parameters. I could probably make a case for DL where we should place
> hooks in admission control path (or somewhere else when more
> sophisticated mechanisms we'll be in place) rather then in the
> periodic
> tick.
We did experiments using util/max in intel_pstate. For some benchmarks
there were regression of 4 to 5%, for some benchmarks it performed at
par with getting utilization from the processor. Further optimization
in the algorithm is possible and still in progress. Idea is that we can
change P-State fast enough and be more reactive. Once I have good data,
I will send to this list. The algorithm can be part of the cpufreq
governor too.

Thanks,
Srinivas